In many electronic warfare applications, it is desirable determine the location of a certain distantly located signal emitter. Such a determination may be made in relative terms with respect to a known reference position and may also be transferred from this relative position to a fixed or global position with the aid of additional processing. In making such position determinations, the angle of arrival (AOA) of the distant signal with respect to a present reference frame is often used as an intermediary step in determining a range vector connecting the present reference location and the distant signal source. Even where it is possible to interpret data relating to the angle of arrival with significant accuracy (for example where a desirable electronically implemented algorithm is available), the relative locations of the receiving antennas used in collecting this data significantly determines the accuracy of the overall distant signal locating process. If the vectors connecting the receiving antennas are determined with errors, these errors can cause enormous emitter location determination errors.
As shown in FIG. 1, the distance between two electronic warfare receiving antennas 102 and 104 disposed on the same platform or aircraft 100 is very short in comparison with the range distance 108 to the signal emitter 106. For example, the distance between the two aircraft-wing mounted antennas 102 and 104 in FIG. 1 can be in the range of tens of meters, even for the largest of possible host aircraft, while the range 108 to the electronic warfare emitter can be hundreds of kilometers in a typical scene. Let us assume for example that the FIG. 1 distance between the antennas 102 and 104 is ten meters and the range 108 is one hundred kilometers. Under these conditions a one-millimeter error in the believed location of an antenna 102 or 104 can cause approximately a 10 meter error in the determination of range 108 (the distance ratios being 10,000 in each instance). Therefore in order to minimize such error, the vector between the electronic warfare antennas 102 and 104 must be measured very accurately.
From this discussion it may be appreciated that differing arrangements of the FIG. 1 measuring event may require the use of either a single electronic warfare antenna on the aircraft 100 or multiple of such antennas. FIG. 1 and the discussion in the preceding paragraph thus may be interpreted to imply that a plurality of electronic warfare antennas, especially two such antennas, are so included and that it is the distance between the effective electrical center point of these antennas that is of a major accuracy concern in the invention. While these implications and interpretations are justified and indeed provide a most easily appreciated understanding of the invention, it should be realized that the invention is not limited to such a two antenna situation and that it may also extend to a single antenna and to the more than two antennas situations where even the instantaneous global positions of a single or more than two movable platform antennas are of concern because of their possible effect on distant signal source location determinations.
According to the present state of the electronic warfare art the locations of antennas such as the FIG. 1 antennas 102 and 104 used for electronic warfare purposes are determined using global position system receivers and the overall capabilities residing in the global position system. In this present art arrangement an electronic warfare antenna location vector is determined from measurements accomplished using an additional global position system antenna that is dedicated to this specific purpose; i.e., a global position system antenna is placed physically close to each electronic warfare antenna under consideration and the relative positions of the global position system antennas are then measured accurately by global position system techniques. Once the location of each thus added global position system antenna is measured, the vector between the electronic warfare antennas can be determined—by physical measurements for example.
In addition to the added complexity of supplying, mounting and measuring associated with the added global position system antennas used in this present state of the electronic warfare art, this procedure can also encounter measurement error as a result of the phase center or the electrical center of the electronic warfare antenna being located in a position differing significantly from the physical center of the antenna. The present invention is believed to provide an arrangement overcoming each of these difficulties with the present state of the electronic warfare art and the determination of a vector between electronic warfare antennas.